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Comparison and Analysis of Atmospheric Turbulence in Free Space Optical Communication for Srinagar

International Journal of Trend in Scientific Research and Development (IJTSRD)
Volume 4 Issue 3, April 2020 Available Online: www.ijtsrd.com e-ISSN: 2456 – 6470
Comparison and Analysis of Atmospheric Turbulence in Free
Space Optical Communication for Srinagar
Tabassum Nisar1*, Rashmi Raj2
1Research
Scholar, 2Assistant Professor
Department of Electronics and Communication Engineering,
Universal Institute of Engineering & Technology, Mohali, Punjab
ABSTRACT
Traditional microwave communication systems can no longer support high
bandwidth demand. Telecommunications companies in the country are
therefore investing huge sums of money in laying underground fiber cables for
their backbone network. The challenges these companies face in laying optical
fiber cables include inaccessibility in the 4 major cities. These cities have
already developed infrastructure (i.e. buildings and roads). Therefore digging
and laying cables are very difficult if not impossible in some suburbs. In such
areas, the companies are forced to depend on microwave links. Again, due to
lack of already developed network infrastructure design in the country,
underground fiber cables are destroyed during road constructions. An
alternative to fiber cables in inaccessible areas could be the use of FSO
installation. FSO can be used to provide backup links in the event of fiber cable
destruction or as a backbone network. Free Space Optical (FSO)
communication is the transmission of optical signals through the atmosphere.
To the best of our knowledge, evaluation of FSO performance in the country
has not been investigated to determine its feasibility. This paper seeks to
investigate whether FSO communication implementation is feasible in
Srinagar. However, turbulent atmospheric conditions have impacts on its
performance and therefore hampered its wide spread deployment. In this
paper, we investigate the feasibility of FSO in Srinagar. Atmospheric
attenuation is estimated based on the atmospheric visibility data. Our results
show atmospheric specific attenuation as high as 27.17dB/km in the 1550nm
window, 29.315dB/km in 1300nm window and 35.20dB/km in the 850nm
window. The probability of encountering different atmospheric attenuation
conditions is estimated. Fading loss due to scintillation is investigated using
the lognormal statistical model. It is shown that the margin to compensate for
losses due to scintillation depends on the power scintillation index and the
allowable system outage probability.
How to cite this paper: Tabassum Nisar |
Rashmi Raj "Comparison and Analysis of
Atmospheric
Turbulence in Free
Space
Optical
Communication for
Srinagar" Published
in
International
Journal of Trend in
IJTSRD30317
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(ijtsrd), ISSN: 2456-6470, Volume-4 |
Issue-3, April 2020, pp.167-170, URL:
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Copyright © 2020 by author(s) and
International Journal of Trend in Scientific
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/4.0)
KEYWORDS: FSO, Specific Attenuation, Fading Loss
INTRODUCTION
The field of wireless communication has been extensively
researched in order to exploit the advantages it has over
wired networks such as mobility and flexibility. The demand
for bandwidth on wireless communication systems today is
increasing at an exponential rate. Many bandwidth
demanding applications (multimedia) are being developed
these days. Thus traditional voice communication is not the
only requirement of wireless communication in today’s
network. The main challenge is to design more adaptive and
scalable networks that can provide high data rates to
support the increasing demand for bandwidth. In view of
this, several wireless networks have been developed to
address the demand for high information carrying capacity.
The amount of data that can be transmitted in any
communication system is directly related to the bandwidth
of the carrier which is directly related to the carrier
frequency. Optical signals use a frequency range of 20THz 375THz and could therefore guarantee very high data rates.
Optical communication systems thus promise the highest
possible information carrying capacity. The theoretical
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information carrying capacity of free space optical
communication systems exceeds that of microwave systems.
The information carrying capacity of microwave systems is
the highest so far amongst the available wireless networks.
Free Space Optical (FSO) communication is the transmission
of high speed data over long distances using optical signals
through free space. Free Space Optical (FSO) communication
can be considered as a viable technology for next generation
communication due to its wide range of applications [1, 2].
Some of its applications are links involving satellites (intersatellite communication), High Altitude Platforms (HAPs),
Unmanned
Aerial
Vehicles
(UAVs),
terrestrial
communications, aircraft and ship-to-ship communication.
FSO can be used to provide high data rates in areas where it
is difficult or impossible to lay optical fiber cables. Again, it
can be used in both military and civilian applications [3]. It
can be used to provide temporal links in the event of
disaster. FSO has more advantages over other traditional
wireless technologies (i.e. Microwave systems). First, FSO
can provide higher data rates (several gigabytes of data)
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than that provided by microwave systems. Secondly, it does
not require licensing for its operation. This is a major cost
advantage over microwave links. Again, FSO channels are
highly immune to electromagnetic interference (EMI) and
highly secure with low probability of interception and low
probability of detection (LPI/LPD) properties [4]. However,
FSO has some disadvantages which have hampered its wide
deployment. It has low availability probability due to its
susceptibility to atmospheric weather conditions [5]. The
availability probability of a communication system is the
percentage of time during which the communication link is
operational. The availability probability requirement of
wireless communication systems is 99.999% [6]. The
primary atmospheric processes that affect optical signal
propagation are atmospheric absorption, atmospheric
scattering and index-of-refractive turbulence (Scintillation).
For an optical radiation traversing the atmosphere,
absorption occurs when some of the photons are
extinguished by molecular constituents of the atmosphere
and their energy converted into heat energy leading to loss
of optical power.
visibility was measured every three hours in a day. Thus
eight visibility measurements were collected daily for two
years. For the two years (i.e. years 2018 and 2019), a total of
5840 visibility measurements were collected for Srinagar
under research. Based on the visibility measurements, we
will estimate the level of attenuation in Srinagar and
estimate the probability of encountering such atmospheric
attenuation conditions.
Parameter
Typical Value
Transmit Power
14dBm
Transmit Beam Divergence Angle 2mrad
Wavelength
850nm
Receiver Aperture Diameter
8cm
Receiver Sensitivity
-30dBm
System Losses
2dB
Table 1.1 Typical FSO System Parameters
Atmospheric Specific Attenuation Estimation of
Srinagar:
We have estimated the attenuation caused by the Srinagar
atmosphere based on the visibility measurements using the
Kruse model of equations. The graphs that follow show the
attenuation coefficient, βa( of Srinagar in dB/km. The
specific attenuation is estimated for three optical
wavelengths typically used in commercial FSO systems (i.e.
850nm, 1300nm and 1550nm). On the X-axis, is the time of
the year during which the visibility measurement was taken.
On the Y-axis, is the attenuation (dB/km) estimated for each
visibility measurement taken in the year.
Figure 1.1 Block Diagram of FSO
Fig1.2 Estd. Attenuation coeff for Srinagar at 850nm
Model of Transmission of Optical Signals:
The transmission of optical signals through the atmosphere
can be modeled by the Beer-Lamberts law. The Beer
Lamberts law can be stated as [3]:
The value of the atmospheric attenuation coefficient is
dependent on the optical wavelength λ, (λ) is composed of
both atmospheric absorption and scattering terms and can
be expressed as:
γ(λ)= αm (λ ) + αa(λ) + βm(λ) + βa(λ)
The successful implementation of FSO systems depends
largely on the local atmospheric conditions. Visibility
measurement data for Srinagar were taken from the Indian
Meteorological Agency for analysis [39]. Atmospheric
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Fig1.3 Estd. Attenuation coeff for Srinagar at 1550nm
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International Journal of Trend in Scientific Research and Development (IJTSRD) @ www.ijtsrd.com eISSN: 2456-6470
Fig1.4 Estd. Attenuation coeff for Srinagar at 1300nm
The estimated optical attenuation for Srinagar is shown in
figures 1.2-1.4 for the year 2018. The highest attenuation
estimated for the year 2018 was 21.0031dB/km on
1550nm wavelength, 22.7904dB/km on 1300nm
wavelength and 27.7706dB/km on 850nm wavelength.
The lowest estimated attenuation was 0.1578dB/km on
1550nm wavelength, 0.1983dB/km on 1300nm
wavelength and 0.3446dB/km on 850nm wavelength. An
annual average of 0.7092dB/km on 1550nm wavelength,
0.8374dB/km on 1300nm wavelength and 1.2725dB/km
on 850nm were estimated.
Fig1.5 Estd. Attenuation coeff for Srinagar at 850nm
Fig1.7 Estd. Attenuation coeff for Srinagar at 1300nm
The estimated optical attenuation for Srinagar is shown in
figures 4.6d-f for the year 2019. The highest attenuation
estimated for the year 2019 was 27.1750dB/km on 1550nm
wavelength, 29.3154dB/km on 1300nm wavelength and
35.2074dB/km on 850nm wavelength. The lowest estimated
attenuation was 0.2209dB/km on 1550nm wavelength,
0.2777dB/km on 1300nm wavelength and 0.4824dB/km on
850nm wavelength. An annual average of 0.5598dB/km on
1550nm wavelength, 0.7165dB/km on 1300nm wavelength
and 1.1143B/km on 850nm were estimated.
Conclusion:
In Srinagar, the highest attenuation estimated was
27.1750dB/km using 1550nm wavelength system,
29.3154dB/km on 1300nm wavelength system and
35.2074dB/km on 850nm wavelength system. The lowest
attenuation estimated was 0.1578dB/km on 1550nm
wavelength, 0.1983dB/km on 1300nm wavelength and
0.3446dB/km on 850nm wavelength. The average
attenuation estimated was 0.6545dB/km on 1550nm
wavelength, 0.7770dB/km on 1300nm wavelength and
1.1934dB/km on 850nm wavelength.
ACKNOWLEDGEMENT
I express my sincere gratitude to the I.K.Gujral Punjab
Technical University, Jalandhar for giving me the
opportunity to work on the thesis during my final year of
M.Tech. I owe my sincerest gratitude towards Dr. Prabhjot
Kaur, Director Engg, Universal Institute of Engineering
and Technology, Lalru, for valuable advice and healthy
criticism throughout my thesis which helped me
immensely to complete my work successfully.
I would like to express a deep sense of gratitude and
thanks profusely to Er. Rashmi Raj Assistant Professor,
Department of Electronics & Communication Engineering,
UIET, who was the thesis Supervisor. Without the wise
counsel and able guidance, it would have been impossible
to complete the thesis in this manner.
I would like to thank the members of the Departmental
Research Committee for their valuable suggestions and
healthy criticism during my presentation of the work. I
express gratitude to other faculty members of Electronics &
Communication Engineering Department, UIET, for their
intellectual support throughout the course of this work.
Fig1.6 Estd. Attenuation coeff for Srinagar at 1550nm
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